[JJ_SO]

It not only sounds heavy, but is, yes. Matt Granger's comparison on YouTube is also interesting (not for Canon users though, they have not much of alternatives) and he prefers his Nikkor. While admitting to be biased because he already owns it, his biggest issue wasn't the performance as he saw of both nearly the same IQ. He had troubles with handholding it for an hour or so.

I don't recall to ever have used one lens for a full hour, but the weight can be a deal breaker. But then, the 85/1.4 Art is only 400 grams less and longer. Funnily, the Otus 85/1.4 has the same weight.

At the moment I'm figuring out how to rent both lenses at the same time to compare them for myself. And to find out if for me, who shot most portraits with an 85, the 105 is an option - or even a better option.

Tamron? Well, I tried their 85/1.8. At f/2 it doesn't come close to the Sigma wide open, was my impression. Take it with a grain of salt: I had no chance to focus adjust it, but in a face and at 1/4000 should some parts be in focus...

I think Sigma lenses - at least the Art types - are already capable of 100 MP, but who wants 100 MP in a FF sensor? Even if it's doable - I have doubts it would be practical, as long as ISO and noise performance will not be significantly improved.